A cascade scanning optical system which includes: a pair of laser scanning optical systems each having a laser beam emitter and a laser beam deflector, wherein a laser beam emitted by the laser beam emitter enters the laser beam deflector so that the laser beam deflector deflects the laser beam to scan a surface of a member such that the laser beams proceed to the surface on a common line thereon in respective ranges of the common line; a pair of mirrors respectively provided in the pair of laser scanning optical systems, each of the pair of mirrors being positioned in a corresponding optical path between the laser beam deflector and the member to reflect a laser beam incident thereon toward the surface; a pair of cylindrical lenses having power in a sub-scanning direction, respectively provided in the pair of laser scanning optical systems, each of the pair of cylindrical lenses being positioned in a corresponding optical path between the laser beam emitter and the laser beam deflector; first means for adjusting an angle of at least one of the pair of mirrors relative to the surface; and second means for adjusting a position of at least one of the pair of cylindrical lenses relative to a corresponding one of the laser beam deflectors.